Concepts for Stirling radioisotope generators have been proposed that would meet requirements for both Mars surface and deep space missions. This paper, based partially on system studies conducted for the department of energy, space and defense power systems, describes a Stirling concept that includes innovative features to maximize specific power, improve reliability, and facilitate integration with either a deep-space mission spacecraft or a Mars rover. A typical power system consists of two or more generators, each generator incorporating opposed pairs of Stirling engine/alternators and heat sources, and a controller that regulates and conditions the electrical power from AC to DC. Some of the innovative features of the proposed generator design include a separate isotope heat source for each engine/alternator, and composite structures that incorporate annealed pyrolytic graphite for high thermal conductance. The resulting configuration is modular in design, low in mass, and compact, with user interfaces that are similar to those of familiar radioisotope thermoelectric generators (RTG) used on Galileo, Ulysses, and Cassini missions. For applications on the Martian surface, the proposed generator concept includes provisions for active cooling during launch, cruise and landing on the Martian surface, and a mounting arrangement that minimizes the impact of dust accumulation.